xcode上未声明的标识符

Question

I just got to start developing for ios 6 on xcode. But as a novice developer, i have come into a problem. Following the guide in the book 'beginning ios5 development: exploring the ios sdk' on chapter 3, the 'Button fun' example.

I am having problems with the identifier 'statusText' which i have already declared in the .h code.

Here's my code so far, any help would be highly appreciated. thank you in advance.

my BIDViewController.h is like so

#import <UIKit/UIKit.h>

@interface BIDViewController : UIViewController
@property (weak, nonatomic) IBOutlet UILabel *
statusText;
- (IBAction)buttonPress:(UIButton *)sender;

@end`

and my BIDViewController.m is like so

#import "BIDViewController.h"

 @interface BIDViewController ()

 @end

 @implementation BIDViewController

 - (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
 }

 - (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

 - (IBAction)buttonPress:(UIButton *)sender {
    NSString *title = [sender titleForState:<#(UIControlState)#>];
    statusText.text = [NSString stringWithFormat:@"%@ button pressed.", title];
}
@end

i have followed the book but can't seem to understand why this occurs, pls help.

Answer 1

Well, for starters, this should be only one line

@property (weak, nonatomic) IBOutlet UILabel *statusText;

Now, when you declare a property, you don't get a variable named like that unless you synthesize it like this:

@implementation Class

@synthesize propertyName;

@end

That's why statusText doesn't exist.

You have three options:

1. Synthesize statusText like that so you can use that ivar.
2. instead of accessing the var directly, access the property like this self.statusText .
3. XCode is creating it's own variable, it's probably named _statusText , access it like that to access the variable directly.

You can also use a combination of 2 and 3

Answer 2

I am using the same book and had that problem, too. I have learned to use an underscore in the .m file

- (IBAction)buttonPressed:(UIButton *)sender {
    NSString *title = [sender titleForState:UIControlStateNormal];
    **_statusText**.text = [NSString stringWithFormat:@"%@ button pressed.", title];

}